This invention relates to a storage system.
Storage systems are demanded to have a high availability (HA) function, which is provided by giving a storage apparatus a cluster configuration. With the HA function, a storage system attains high availability. An HA configuration has double systems and, when a failure occurs in one of the systems, automatically cuts off the failed system to continue operating using the normal system alone. The HA function further accomplishes full use of resources and load balancing by running two systems as active systems.
In order to maintain consistency between the systems of the HA configuration, volumes of the double systems are synchronized with each other. A pair of a volume belonging to one system and a volume belonging to the other system is called an HA pair. Writing in write processing is completed only after data is written in the two volumes. It therefore takes long to respond to a host.
The distance between the volumes of an HA pair may be set relatively short in a business operation that places importance on response performance. In this case, both of two storage apparatus may be rendered unusable when a disaster affecting a wide area occurs. Another issue is that data safety drops when a failure occurs in one of the systems of the HA configuration and the normal system continues operating alone. Data safety can be enhanced by creating a backup in a distant data center through remote copying.
Patent Literature 1 can be given as background art for attaining high availability of a storage system. In Abstract of Patent Literature 1, there is a disclosure that: “The same virtual identifier is set for volume 1A of a first storage unit 1 and for a volume 2A of a second storage unit 2. A path control unit 5B of a host 5 identifies the volumes 1A and 2A, which have the same virtual identifier, as one virtual volume 6. A remote copy pair can also be set by a virtual volume 6 and a volume 3A of a third storage unit 3.”
In Patent Literature 1, when a failure occurs in the first storage unit, failover from the first storage unit to the second storage unit is executed to continue the business operation. After the second storage unit starts running, an update to data in the second storage unit is reflected in the third storage unit by remote copy. This enables the third storage unit to take over the business operation of the second storage unit if a further failure occurs in the second storage unit.
Patent Literature 1: US 2009/0094403 A1